Counterbalance devices are used in weight lifting operations to oppose a load, weight or force For example, in a sheet metal stamping press, it is necessary to move a platen and the die and tooling thereon which depending on its size and design, usually weighs about 5,000 pounds to 25,000 pounds. The platen and die and tooling is raised and lowered usually through a distance of 18" to 24", and at a relatively rapid rate of one to two seconds per cycle The counterbalance reduces, usually by 80% to 90% the power required to rapidly move this load which, without a counterbalance, typically would be about 100 to 300 horsepower.
A counterbalance system provides a source of potential energy which is utilized to counteract gravity acting on the movable platen, and the die and tool secured to it. Usually, the counterbalance system has a surge tank connected to one or more air cylinders, and preferably an air regulator to control and maintain the desired pressure of the compressed gas or other fluid in the system. The surge tank has sufficient volume so that as the cylinders are cycled, the pressure of the gas in the system does not change dramatically due to varying the effective volume of the cylinders. The cylinders convert the pressurized gas into a force which opposes the weight or effect of gravity on the movable platen and the die and tooling secured to it. Each cylinder is of conventional design with a piston and a rod slidably received in a head or cap. The rod is slidably received in a bearing and a seal assembly rigidly carried by the head.
The load is lifted or carried by the rod in a manner requiring the axis of the rod to be parallel and essentially coincident with the path of movement of the load In case of improper alignment, the rod may be bent, the piston may be tilted or cocked and thereby damage the piston, seals or interior surface of the cylinder wall, and/or the radial loading on the various cylinder parts may produce rapid wear and a short useful life.
Typically, to avoid such damage, a gimbal device is used to permit the cylinder to align itself and hence the rod with the path of movement of the load which is operably connected to the rod by the counterbalancing device Gimbals, for this application, are complex and expensive. Moreover, flexible rubber hoses are required to supply compressed air or other actuating fluid to the cylinder.